1. Field of the Invention
This invention relates to a method and apparatus for building thickened ice masses for offshore operations in cold water, and particularly to a method and apparatus for building ice islands suitable for use as work platforms in cold offshore locations.
2. Description of the Prior Art
In the continuing search for new petroleum and natural gas reservoirs, considerable interest has recently been focused on exploration and production activities in the arctic and antarctic regions of the world. In these areas, subterranean formations having potential for petroleum and/or natural gas accumulations are sometimes found underlying ice-covered offshore locations which have relatively shallow waters. Conventional floating platforms are not well suited for operations in these waters.
Various types of bottom-supported platforms have been suggested for use in these offshore locations including platforms constructed from steel, concrete and/or fill material dredged from the marine bottom. These platforms are relatively expensive to construct and are expensive to remove after the operations are terminated.
Ice has been proposed for use as the construction material for bottom-supported platforms. Grounded ice islands can be constructed by depositing water over a natural ice sheet to thicken the ice mass until its draft is greater than the water depth and at least part of the thickened ice mass is grounded on the marine bottom. U.S. Pat. No. 4,048,808 to Duthweiler, U.S. Pat. No. 3,863,456 to Durning and U.S. Pat. No. 3,849,993 to Robinson et al. disclose methods for building ice islands in which water is sprayed or flowed onto a natural ice sheet to form a grounded ice island.
Ice islands appear to be feasible for use as work platforms from which to conduct operations such as exploratory drilling, and perhaps, under the proper conditions, for year-around drilling and/or production. However, in most of the offshore areas which are candidates for the use of ice islands, the natural ice sheet and ice island will break up and melt during the warmer summer months. The time available for construction of the ice island and drilling of the well is often limited to five months or less and the time available is rarely more than eight months. A major portion of this time has been found to be required for the construction of the ice island, primarily due to the adverse working conditions and the limits of the apparati which have been used to build up the ice mass. For example, an ice island constructed by flooding water onto an enclosed area between snow berms on the natural ice sheet using manually controlled water pumps required more than two months to build. After the drilling rig was installed, only about two months remained to complete the drilling program before the drilling rig had to be removed. A need exists for a method and apparatus for more quickly building an ice island in order to allow more time for completion of the operations to be conducted from the ice island.
Accordingly, it is a primary object of this invention to provide a method and apparatus for rapidly constructing ice islands at cold offshore locations.
Another object of this invention is to provide an improved method and apparatus for building ice islands in a manner which is substantially unaffected by the adverse weather conditions and physical constraints which hindered rapid construction of ice islands with the prior art methods and apparati.
Yet another object of the invention is to provide a substantially completely mechanized apparatus and method for quickly building ice islands at cold offshore locations.
A further object of this invention is to provide an improved method and apparatus for building an ice island in a substantially continuous mechanized manner to thereby reduce the time required to complete the ice island construction.
Still further objects, advantages and features of the invention will become apparent to those skilled in the art from the following description taken in conjunction with the accompanying drawings.